Thermodynamic analysis of the effect of molten steel compositions on tin removal

Abstract

Residual elements are always introduced by raw materials in the ferrous metallurgy process, and some of them can not be effectively removed by the conventional steelmaking process. Tin as one of the common residual elements in steel will cause the performance deteriorations of steel. The calcium treatment process is indicated that it has good efficiency for removing tin from molten steel. However, the thermodynamic relationships between tin and other compositions in molten steel are not very clear. In this study, the thermodynamic database software Factsage7.0 was applied to study the influences of calcium, oxygen and sulfur contents on tin removal, and the equilibrium concentration of calcium-tin in molten steel was calculated. The results show that tin removal in molten steel should be under the reduction condition, and the critical calcium content increases with the improvement of the contents of oxygen and sulfur, however, it decreases with the increase of tin content. The lower temperature is helpful to tin removal. In addition, the oxygen content must be reduced firstly, and then the sulfur content should also be decreased to ensure the possibility of tin removal. For the selected steel grade, the calculated result of the calcium-tin equilibrium concentration product shows that it is equal to a constant at a certain temperature.